It is well known that an oligoribonucleic acid (oligo-RNA) is useful as a RNA probe for genetic analysis, a material for a RNA drug product (an antisense RNA, a ribozyme, or an RNA species that regulates gene expression through the RNAi effect), an artificial enzyme, or an aptamer.
As one of the reagents for producing an oligo-RNA, a phosphoramidite compound in which the 2′-hydroxyl group of a ribose is protected by substitution by a CEM group which can be removed under neutral conditions is known (Non-patent document 1).
In cases where an oligo-RNA is produced by using the above-mentioned phosphoramidite compound, after an oligo-RNA having a desired chain length is produced on a solid-phase support, it is necessary to remove the oligo-RNA from the solid-phase support and to remove the protecting group for each substituent from the oligo-RNA. One of the steps of removing such a protecting group is the step of removing an ether-type protecting group, which protects the 2′-hydroxyl group of each ribose of an oligo-RNA and can be removed under neutral conditions. In the step, tetrabutylammonium fluoride (hereinafter referred to as “TBAF”) is generally used as a deprotecting agent, and tetrahydrofuran (hereinafter referred to as “THF”) is used as a solvent (Non-patent document 1).    Non-patent document 1: Ohgi et al., Organic Letters, Vol. 7, 3477 (2005)